A level crossing is an intersection where a railway line crosses a road or path at the same level, as opposed to railway line crossings using bridges or tunnels. The safety of level crossings is one of the most important issues of railways services. Each year about 400 people in the European Union and over 300 in the United States are killed in level crossing accidents. Collisions can occur with vehicles as well as pedestrians; pedestrian collisions are more likely to result in death.
As far as warning systems for road users are concerned, standard level crossings have either passive protections in the form of different types of warning signs, or active protections, using automatic warning devices such as flashing lights, warning tones and boom gates. Fewer collisions take place at level crossings with active warning systems.
Recently, railroad companies have started to control level crossings through wireless control systems of the trains (e.g. ITCS, ETCS, I-ETMS etc.), because this approach provides many benefits.
In these systems, a signal is wirelessly sent from a control unit of the train towards a control unit associated to the level crossing, thus allowing the latter to properly control the opening or closing of bars or gates placed in correspondence of the level crossing and arranged to prevent the crossing of the level crossing by vehicles or pedestrians present on the intersecting road or path.
This way of controlling the level crossings allows operations to be performed at speeds higher than the traditional activation through track circuits.
Level crossings operated through track circuits activate the crossing based either on initial occupancy of a section of track, or on detection of motion in any section of a track, or on prediction of arrival time based on changes in the electrical impedance of a track measured between the level crossing and the lead axle of the train.
All these track circuit methods have physical limitations as to how far from the crossing they can detect the train.
If a minimum amount of warning time is required for correctly closing the bars of a level crossing, then there is an upper limit to the maximum speed of the train at which track circuits can effectively and timely provide this warning time.
Wireless activation also enables constant warning prediction in areas where it was not previously possible (e.g. electrified rails, areas of poor shunting, etc.).
In some cases, railroad companies have considered to completely eliminate the activation of level crossing through track circuits and to operate them (namely, the bars present in correspondence of level crossings) through wireless activation only.
In fact, track circuits used to operate the bars represent a big expense for companies as they require constant adjustment and maintenance, and numerous train delays occur due to poor operation in harsh environmental conditions or when the track wires are damaged by the track maintenance equipment.
While the wireless level crossing activation potentially enables the elimination of the track circuits, the island track circuit is still required to keep the bars down when a train occupies a short area of a railway track placed on both side of a road.
In fact, a track circuit controlled level crossing generally has two different track circuits: one approach circuit and one island circuit.
The approach track circuit is a long distance circuit looking for the initial approach of the train, for the purpose of activating the warning devices. Any activation of the warning devices from the approach track circuit may be cleared if the train stops short of the crossing.
The island track circuit is a short distance circuit, that keeps the warning devices activated any time this circuit is occupied by any portion of the train.
The main drawback of these existing circuits is that they require both constant adjustment and maintenance and a wired connection to the rails, which is commonly damaged by track maintenance equipment.
As a result, the train movements are restricted until these wired connections are repaired and the level crossing equipment is tested and restored.
There is therefore the need to replace such island track circuits with a solution that is however capable of providing a SIL-4 (Safety Integrity Level) train detection, with a reliability equivalent to the one of the solution based on the island track circuits but that, on the other side, does not require wires attached to the rails or equipment in the fouling zone wherein a fouling zone is an area where track maintenance equipments may damage devices of the railway track.